* Investors Grenzebach and Wyser-Pratte get upper hand
* Shares jump more than 10 percent
(Adds departures, updates share price)
FRANKFURT, Sept 3 (Reuters) - The chairman, chief executive and chief financial officer of German robotics group Kuka stepped down on Thursday, handing victory to rebel investors in a power struggle.
Four supervisory board members including Chairman Rolf Bartke will resign on Sept. 18, the company said after an extraordinary supervisory board meeting.
CEO Horst Kayser and CFO Matthias Rapp will depart on Sept. 30 by mutual consent with the board, a statement said.
The exodus gives large shareholders Grenzebach and Guy Wyser-Pratte freedom to nominate their own representatives.
"Shareholder Grenzebach Maschinenbau GmbH stated that it will file a petition for judicial appointment of three members of the supervisory board. The new executive board of the company shall be appointed until September 30, 2009," Kuka said.
Kuka shares advanced 10.3 percent to 11.85 euros by 1359 GMT, the leading gainers among German midcap stocks.
The jump follows German newspaper reports that wholesale changes at the top of Kuka were imminent.
"The reports could help churn up M&A speculation, although I don't know how long this speculation will last," said one Frankfurt-based trader.
"The news may act positively on hopes more radical measures to improve profits may drive the share price and as speculation increases that shareholders Grenzebach and Wyser-Pratte might raise their stakes," the trader added.
Grenzebach holds 29.2 percent in Kuka while Wyser-Pratte holds nearly 10 percent. (Reporting by Michael Shields and Tyler Sitte; Editing by David Holmes)